Actually, Amateur Pie (Topcash), DOES have signup ratios, they boast that they don't, but if you fall out of a 1:1500 ratio, they'll switch ya over.
Amateur Pages is the best, go with them for banner ads.
If you want another great sponsor to use, you should go with NexCash -
http://www.nex-cash.com/index.asp?rid=21313 They pay 2.5-3.5 cents per click depending on the amount of traffic that you send them. They have NO ratios and you can link them up any way that you like. You can even use MOUSEOVER links or put their links inside of consoles on your page, so that's nice. The visitor has to click into their page from the first link, but a lot of people do and I make some pretty good money with them and they've been paying me for the last few months, so give them a shot.